/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package io.nop.job.core.utils;

import io.nop.api.core.exceptions.NopException;
import io.nop.commons.util.StringHelper;

import javax.annotation.Nullable;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.Calendar;
import java.util.Collections;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.List;
import java.util.TimeZone;

import static io.nop.job.core.JobCoreErrors.ARG_CRON_EXPR;
import static io.nop.job.core.JobCoreErrors.ERR_JOB_TRIGGER_PARSE_CRON_EXPR_FAIL;

/**
 * Date sequence generator for a <a href="https://www.manpagez.com/man/5/crontab/">Crontab pattern</a>, allowing clients
 * to specify a pattern that the sequence matches.
 *
 * <p>
 * The pattern is a list of six single space-separated fields: representing second, minute, hour, day, month, weekday.
 * Month and weekday names can be given as the first three letters of the English names.
 *
 * <p>
 * Example patterns:
 * <ul>
 * <li>"0 0 * * * *" = the top of every hour of every day.</li>
 * <li>"*&#47;10 * * * * *" = every ten seconds.</li>
 * <li>"0 0 8-10 * * *" = 8, 9 and 10 o'clock of every day.</li>
 * <li>"0 0 6,19 * * *" = 6:00 AM and 7:00 PM every day.</li>
 * <li>"0 0/30 8-10 * * *" = 8:00, 8:30, 9:00, 9:30, 10:00 and 10:30 every day.</li>
 * <li>"0 0 9-17 * * MON-FRI" = on the hour nine-to-five weekdays</li>
 * <li>"0 0 0 25 12 ?" = every Christmas Day at midnight</li>
 * </ul>
 *
 * @author Dave Syer
 * @author Juergen Hoeller
 * @author Ruslan Sibgatullin
 * @since 3.0
 */
public class CronExpression implements ICronExpression {

    private final String expression;

    private final TimeZone timeZone;

    private final BitSet months = new BitSet(12);

    private final BitSet daysOfMonth = new BitSet(31);

    private final BitSet daysOfWeek = new BitSet(7);

    private final BitSet hours = new BitSet(24);

    private final BitSet minutes = new BitSet(60);

    private final BitSet seconds = new BitSet(60);

    /**
     * Construct a {@link CronExpression} from the pattern provided, using the default {@link TimeZone}.
     *
     * @param expression a space-separated list of time fields
     * @throws IllegalArgumentException if the pattern cannot be parsed
     * @see java.util.TimeZone#getDefault()
     */
    public CronExpression(String expression) {
        this(expression, TimeZone.getDefault());
    }

    /**
     * Construct a {@link CronExpression} from the pattern provided, using the specified {@link TimeZone}.
     *
     * @param expression a space-separated list of time fields
     * @param timeZone   the TimeZone to use for generated core times
     * @throws IllegalArgumentException if the pattern cannot be parsed
     */
    public CronExpression(String expression, TimeZone timeZone) {
        this.expression = expression;
        this.timeZone = timeZone == null ? TimeZone.getDefault() : timeZone;

        try {
            parse(expression);
        } catch (Exception e) {
            throw new NopException(ERR_JOB_TRIGGER_PARSE_CRON_EXPR_FAIL).param(ARG_CRON_EXPR, expression);
        }
    }

    private CronExpression(String expression, String[] fields) {
        this.expression = expression;
        this.timeZone = null;
        doParse(fields);
    }

    public TimeZone getTimeZone() {
        return timeZone;
    }

    /**
     * Return the cron pattern that this sequence generator has been built for.
     */
    public String getExpression() {
        return this.expression;
    }

    /**
     * Get the next {@link Date} in the sequence matching the Cron pattern and after the value provided. The return
     * value will have a whole number of seconds, and will be after the input value.
     *
     * @param date a seed value
     * @return the next value matching the pattern
     */
    public long getTimeAfter(long date) {
        /*
         * The plan:
         *
         * 1 Start with whole second (rounding up if necessary)
         *
         * 2 If seconds match move on, otherwise find the next match: 2.1 If next match is in the next minute then roll
         * forwards
         *
         * 3 If minute matches move on, otherwise find the next match 3.1 If next match is in the next hour then roll
         * forwards 3.2 Reset the seconds and go to 2
         *
         * 4 If hour matches move on, otherwise find the next match 4.1 If next match is in the next day then roll
         * forwards, 4.2 Reset the minutes and seconds and go to 2
         */

        Calendar calendar = new GregorianCalendar();
        calendar.setTimeZone(this.timeZone);
        calendar.setTimeInMillis(date);

        // First, just reset the milliseconds and try to calculate from there...
        calendar.set(Calendar.MILLISECOND, 0);
        long originalTimestamp = calendar.getTimeInMillis();
        doNext(calendar, calendar.get(Calendar.YEAR));

        if (calendar.getTimeInMillis() == originalTimestamp) {
            // We arrived at the original timestamp - round up to the next whole second and try again...
            calendar.add(Calendar.SECOND, 1);
            doNext(calendar, calendar.get(Calendar.YEAR));
        }

        return calendar.getTimeInMillis();
    }

    private void doNext(Calendar calendar, int dot) {
        List<Integer> resets = new ArrayList<>();

        int second = calendar.get(Calendar.SECOND);
        List<Integer> emptyList = Collections.emptyList();
        int updateSecond = findNext(this.seconds, second, calendar, Calendar.SECOND, Calendar.MINUTE, emptyList);
        if (second == updateSecond) {
            resets.add(Calendar.SECOND);
        }

        int minute = calendar.get(Calendar.MINUTE);
        int updateMinute = findNext(this.minutes, minute, calendar, Calendar.MINUTE, Calendar.HOUR_OF_DAY, resets);
        if (minute == updateMinute) {
            resets.add(Calendar.MINUTE);
        } else {
            doNext(calendar, dot);
        }

        int hour = calendar.get(Calendar.HOUR_OF_DAY);
        int updateHour = findNext(this.hours, hour, calendar, Calendar.HOUR_OF_DAY, Calendar.DAY_OF_WEEK, resets);
        if (hour == updateHour) {
            resets.add(Calendar.HOUR_OF_DAY);
        } else {
            doNext(calendar, dot);
        }

        int dayOfWeek = calendar.get(Calendar.DAY_OF_WEEK);
        int dayOfMonth = calendar.get(Calendar.DAY_OF_MONTH);
        int updateDayOfMonth = findNextDay(calendar, this.daysOfMonth, dayOfMonth, this.daysOfWeek, dayOfWeek, resets);
        if (dayOfMonth == updateDayOfMonth) {
            resets.add(Calendar.DAY_OF_MONTH);
        } else {
            doNext(calendar, dot);
        }

        int month = calendar.get(Calendar.MONTH);
        int updateMonth = findNext(this.months, month, calendar, Calendar.MONTH, Calendar.YEAR, resets);
        if (month != updateMonth) {
            if (calendar.get(Calendar.YEAR) - dot > 4) {
                throw new IllegalArgumentException(
                        "Invalid cron expression \"" + this.expression + "\" led to runaway search for next core");
            }
            doNext(calendar, dot);
        }

    }

    private int findNextDay(Calendar calendar, BitSet daysOfMonth, int dayOfMonth, BitSet daysOfWeek, int dayOfWeek,
                            List<Integer> resets) {

        int count = 0;
        int max = 366;
        // the DAY_OF_WEEK values in java.util.Calendar start with 1 (Sunday),
        // but in the cron pattern, they start with 0, so we subtract 1 here
        while ((!daysOfMonth.get(dayOfMonth) || !daysOfWeek.get(dayOfWeek - 1)) && count++ < max) {
            calendar.add(Calendar.DAY_OF_MONTH, 1);
            dayOfMonth = calendar.get(Calendar.DAY_OF_MONTH);
            dayOfWeek = calendar.get(Calendar.DAY_OF_WEEK);
            reset(calendar, resets);
        }
        if (count >= max) {
            throw new IllegalArgumentException("Overflow in day for expression \"" + this.expression + "\"");
        }
        return dayOfMonth;
    }

    /**
     * Search the bits provided for the next set bit after the value provided, and reset the calendar.
     *
     * @param bits        a {@link BitSet} representing the allowed values of the field
     * @param value       the current value of the field
     * @param calendar    the calendar to increment as we move through the bits
     * @param field       the field to increment in the calendar (@see {@link Calendar} for the static constants defining valid
     *                    fields)
     * @param lowerOrders the Calendar field ids that should be reset (i.e. the ones of lower significance than the field of
     *                    interest)
     * @return the value of the calendar field that is next in the sequence
     */
    private int findNext(BitSet bits, int value, Calendar calendar, int field, int nextField,
                         List<Integer> lowerOrders) {
        int nextValue = bits.nextSetBit(value);
        // roll over if needed
        if (nextValue == -1) {
            calendar.add(nextField, 1);
            reset(calendar, Collections.singletonList(field));
            nextValue = bits.nextSetBit(0);
        }
        if (nextValue != value) {
            calendar.set(field, nextValue);
            reset(calendar, lowerOrders);
        }
        return nextValue;
    }

    /**
     * Reset the calendar setting all the fields provided to zero.
     */
    private void reset(Calendar calendar, List<Integer> fields) {
        for (int field : fields) {
            calendar.set(field, field == Calendar.DAY_OF_MONTH ? 1 : 0);
        }
    }

    // Parsing logic invoked by the constructor

    /**
     * Parse the given pattern expression.
     */
    private void parse(String expression) throws IllegalArgumentException {
        String[] fields = StringHelper.tokenizeToStringArray(expression, " ");
        if (!areValidCronFields(fields)) {
            throw new IllegalArgumentException(String.format(
                    "Cron expression must consist of 6 fields (found %d in \"%s\")", fields.length, expression));
        }
        doParse(fields);
    }

    private void doParse(String[] fields) {
        setNumberHits(this.seconds, fields[0], 0, 60);
        setNumberHits(this.minutes, fields[1], 0, 60);
        setNumberHits(this.hours, fields[2], 0, 24);
        setDaysOfMonth(this.daysOfMonth, fields[3]);
        setMonths(this.months, fields[4]);
        setDays(this.daysOfWeek, replaceOrdinals(fields[5], "SUN,MON,TUE,WED,THU,FRI,SAT"), 8);

        if (this.daysOfWeek.get(7)) {
            // Sunday can be represented as 0 or 7
            this.daysOfWeek.set(0);
            this.daysOfWeek.clear(7);
        }
    }

    /**
     * Replace the values in the comma-separated list (case insensitive) with their index in the list.
     *
     * @return a new String with the values from the list replaced
     */
    private String replaceOrdinals(String value, String commaSeparatedList) {
        String[] list = StringHelper.commaDelimitedListToStringArray(commaSeparatedList);
        for (int i = 0; i < list.length; i++) {
            String item = list[i].toUpperCase();
            value = StringHelper.replace(value.toUpperCase(), item, "" + i);
        }
        return value;
    }

    private void setDaysOfMonth(BitSet bits, String field) {
        int max = 31;
        // Days of month start with 1 (in Cron and Calendar) so add one
        setDays(bits, field, max + 1);
        // ... and remove it from the front
        bits.clear(0);
    }

    private void setDays(BitSet bits, String field, int max) {
        if (field.contains("?")) {
            field = "*";
        }
        setNumberHits(bits, field, 0, max);
    }

    private void setMonths(BitSet bits, String value) {
        int max = 12;
        value = replaceOrdinals(value, "FOO,JAN,FEB,MAR,APR,MAY,JUN,JUL,AUG,SEP,OCT,NOV,DEC");
        BitSet months = new BitSet(13);
        // Months start with 1 in Cron and 0 in Calendar, so push the values first into a longer bit set
        setNumberHits(months, value, 1, max + 1);
        // ... and then rotate it to the front of the months
        for (int i = 1; i <= max; i++) {
            if (months.get(i)) {
                bits.set(i - 1);
            }
        }
    }

    private void setNumberHits(BitSet bits, String value, int min, int max) {
        String[] fields = StringHelper.delimitedListToStringArray(value, ",");
        for (String field : fields) {
            if (!field.contains("/")) {
                // Not an incrementer so it must be a range (possibly empty)
                int[] range = getRange(field, min, max);
                bits.set(range[0], range[1] + 1);
            } else {
                String[] split = StringHelper.delimitedListToStringArray(field, "/");
                if (split.length > 2) {
                    throw new IllegalArgumentException("Incrementer has more than two fields: '" + field
                            + "' in expression \"" + this.expression + "\"");
                }
                int[] range = getRange(split[0], min, max);
                if (!split[0].contains("-")) {
                    range[1] = max - 1;
                }
                int delta = Integer.parseInt(split[1]);
                if (delta <= 0) {
                    throw new IllegalArgumentException("Incrementer delta must be 1 or higher: '" + field
                            + "' in expression \"" + this.expression + "\"");
                }
                for (int i = range[0]; i <= range[1]; i += delta) {
                    bits.set(i);
                }
            }
        }
    }

    private int[] getRange(String field, int min, int max) {
        int[] result = new int[2];
        if (field.contains("*")) {
            result[0] = min;
            result[1] = max - 1;
            return result;
        }
        if (!field.contains("-")) {
            result[0] = result[1] = Integer.parseInt(field);
        } else {
            String[] split = StringHelper.delimitedListToStringArray(field, "-");
            if (split.length > 2) {
                throw new IllegalArgumentException(
                        "Range has more than two fields: '" + field + "' in expression \"" + this.expression + "\"");
            }
            result[0] = Integer.parseInt(split[0]);
            result[1] = Integer.parseInt(split[1]);
        }
        if (result[0] >= max || result[1] >= max) {
            throw new IllegalArgumentException(
                    "Range exceeds maximum (" + max + "): '" + field + "' in expression \"" + this.expression + "\"");
        }
        if (result[0] < min || result[1] < min) {
            throw new IllegalArgumentException(
                    "Range less than minimum (" + min + "): '" + field + "' in expression \"" + this.expression + "\"");
        }
        if (result[0] > result[1]) {
            throw new IllegalArgumentException(
                    "Invalid inverted range: '" + field + "' in expression \"" + this.expression + "\"");
        }
        return result;
    }

    /**
     * Determine whether the specified expression represents a valid cron pattern.
     *
     * @param expression the expression to evaluate
     * @return {@code true} if the given expression is a valid cron expression
     * @since 4.3
     */
    public static boolean isValidExpression(@Nullable String expression) {
        if (expression == null) {
            return false;
        }
        String[] fields = StringHelper.tokenizeToStringArray(expression, " ");
        if (!areValidCronFields(fields)) {
            return false;
        }
        try {
            new CronExpression(expression, fields);
            return true;
        } catch (IllegalArgumentException ex) {
            return false;
        }
    }

    private static boolean areValidCronFields(@Nullable String[] fields) {
        return (fields != null && fields.length == 6);
    }

    @Override
    public boolean equals(@Nullable Object other) {
        if (this == other) {
            return true;
        }
        if (!(other instanceof CronExpression)) {
            return false;
        }
        CronExpression otherCron = (CronExpression) other;
        return (this.months.equals(otherCron.months) && this.daysOfMonth.equals(otherCron.daysOfMonth)
                && this.daysOfWeek.equals(otherCron.daysOfWeek) && this.hours.equals(otherCron.hours)
                && this.minutes.equals(otherCron.minutes) && this.seconds.equals(otherCron.seconds));
    }

    @Override
    public int hashCode() {
        return (17 * this.months.hashCode() + 29 * this.daysOfMonth.hashCode() + 37 * this.daysOfWeek.hashCode()
                + 41 * this.hours.hashCode() + 53 * this.minutes.hashCode() + 61 * this.seconds.hashCode());
    }

    @Override
    public String toString() {
        return getClass().getSimpleName() + ": " + this.expression;
    }

}